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Author Topic:   How big is the Universe?
onifre
Member (Idle past 2950 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 31 of 39 (535854)
11-18-2009 12:29 PM
Reply to: Message 30 by cavediver
11-17-2009 4:32 PM


Re: Imported Universe Response To Onifre
Thanks cavediver,
Just when I think I have some of it figured out, I don't.
Minkowski space-time is the space-time of Special Relativity. Our Universe is not Minkowskian except over small distances. Same way that the ground is not Euclidean (we live on a spheroid) but appears Euclidean over small enough distances.
So what would you describe it as?
I think I know what you are saying here, but the Planck Scale is a scale in the same sense as the atomic scale, and refers to lengths on the order of the Planck Length (1.6 x 10-35) We sometimes use the phrase, *THE* Planck Time, to refer to the earliest moments of the Universe following T=0, but *A* Planck time is simply the geometric length of time, 5.4 x 10-44secs.
I meant that it was finite in size, would that be a correct way to say it?
No, it could well be infinite in extent spatially at all times T>0
Ah, ok.
Is this what you think it is, or do you think (know) that it wraps back up on itself?
For the most part, was my explanation to Buz sorta on point? I hope I don't come off as a know it all, I just like posting my perspective because its the only way you (or SonGoku) can correct me.
- Oni

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Buzsaw
Inactive Member


Message 32 of 39 (535968)
11-18-2009 11:26 PM
Reply to: Message 30 by cavediver
11-17-2009 4:32 PM


Re: Imported Universe Response To Onifre
I appreciate the info from Onifre and Cavediver. I need to study and think on these before further responses.

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Buzsaw
Inactive Member


Message 33 of 39 (535969)
11-18-2009 11:28 PM
Reply to: Message 30 by cavediver
11-17-2009 4:32 PM


Re: Imported Universe Response To Onifre
Accidental double post.
Edited by Buzsaw, : As noted

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DevilsAdvocate
Member (Idle past 3100 days)
Posts: 1548
Joined: 06-05-2008


Message 34 of 39 (535995)
11-19-2009 6:09 AM
Reply to: Message 28 by onifre
11-17-2009 12:55 PM


Re: Imported Universe Response To Onifre
Onifre writes:
What is meant by "spacetime" is a description of the geometry of the universe, ie. Minkowski spacetime. That is finite in size down to Plank scale.
This had an origin, the Big Bang.
I believe the Big Bang Theory explains events that occur after T>0 but does not in itself explain the cause or origin of the spacetime itself.
The origin/cause of the Big Bang is still being hypothesized though Hawkings predicts that our universe, the spacetime we exist in, did not have an origin meaining the concept of time itself cannot have a first cause. Cause and effect are concepts dependent on the concept of time and therefore time is unbounded i.e. it has no one point of origin, as Hawkings predicts. Therefore it makes no sense to say that spacetime had a beginning.
There are other hypothesis/theories that state that our universe (not all of spacetime) had other types of origins i.e. spawned off from other universes (multi-world theory), is part of a large omniverse (the brane), is infinite progression of expansion and collapsing spacetime continuum, etc, or a combination of the above. As we digger deeper into reality we reveal many of these theories are interrelated and have hidden truths that apply.
Just to add another perspective albeit a layman's perspective based on some very limited amount of knowledge.
Edited by DevilsAdvocate, : No reason given.

One of the saddest lessons of history is this: If we've been bamboozled long enough, we tend to reject any evidence of the bamboozle. We're no longer interested in finding out the truth. The bamboozle has captured us. It is simply too painful to acknowledge -- even to ourselves -- that we've been so credulous. - Carl Sagan, The Fine Art of Baloney Detection
"You can't convince a believer of anything; for their belief is not based on evidence, it's based on a deep seated need to believe." - Carl Sagan
"It is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring." - Carl Sagan, The Demon-Haunted World

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jaywill
Member (Idle past 1940 days)
Posts: 4519
From: VA USA
Joined: 12-05-2005


Message 35 of 39 (536287)
11-21-2009 12:20 PM


The question here is how big is the universe ? What a question! I tell you I do not know. I am all ears if anyone can figure it out.
But the problem I see as a theist is this:
No matter how much you subdivide that material universe into smaller and smaller and smaller units even down to the final smallest particle, OR
no matter how you compound the universe into greater and greater super structures on more and more complex levels and super levels ...
the cause of the origin of its existence must be found outside of itself.
This is what the modern mind seems to want to escape. However we theorize its structure or number of dimensions, the cause of the whole thing must lie outside of itself.
No?
Oh okay. What do I know? I'm just a bible thumper.

  
aristarchus
Member (Idle past 307 days)
Posts: 31
Joined: 01-11-2005


Message 36 of 39 (536293)
11-21-2009 2:08 PM
Reply to: Message 6 by cavediver
10-16-2009 8:49 AM


Just so I can be sure that this is as strange as I think it is, what you're saying is that at T=0 the universe is infinite, but after the expansion of TBB it becomes tiny?

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Replies to this message:
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Larni
Member (Idle past 163 days)
Posts: 4000
From: Liverpool
Joined: 09-16-2005


Message 37 of 39 (536297)
11-21-2009 2:28 PM
Reply to: Message 36 by aristarchus
11-21-2009 2:08 PM


what you're saying is that at T=0 the universe is infinite, but after the expansion of TBB it becomes tiny?
I think it's more like the radius of the universe at T=0 is 0 but it contains all that is.

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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


(1)
Message 38 of 39 (536299)
11-21-2009 2:30 PM
Reply to: Message 36 by aristarchus
11-21-2009 2:08 PM


what you're saying is that at T=0 the universe is infinite, but after the expansion of TBB it becomes tiny
No. I'm saying that at T=0, size is undefined, and at T>0 the Universe may be finite (and tiny for small T) or it might be infinite. In the latter case, our observable Universe starts out infinitely small, but the entire Universe is still infinite in extent!

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Replies to this message:
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aristarchus
Member (Idle past 307 days)
Posts: 31
Joined: 01-11-2005


Message 39 of 39 (536333)
11-21-2009 9:27 PM
Reply to: Message 38 by cavediver
11-21-2009 2:30 PM


Thanks for the clarification. I did take notice that you had written that it didn't make sense to talk about the size of the pre BB universe,
but I misinterpreted other things.

This message is a reply to:
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